1. Field of the Invention
The present invention relates to loudspeakers or audio transducers and more particularly to Subwoofers, as used in audio playback and sound reinforcement applications.
2. Discussion of the Prior Art
A great variety of moving coil loudspeaker transducer designs have been proposed for high quality, low frequency sound reproduction. Low frequency transducers or “woofers” are typically included in a modern full range loudspeaker system utilizing different transducers for different segments of the sound spectrum. For example, the “woofer” is used for bass or low frequencies, a mid-range speaker is used for intermediate frequencies and a “tweeter” is used for the highest frequencies in the reproduced spectrum.
It is generally accepted that loudspeakers with sufficient size to produce adequate bass have well understood limitations. In particular, high power signals driving the cone into extreme excursions cause poor sound reproduction when driven by more challenging audio signals.
Typical prior art woofers utilize circular baskets supporting and aiming a frusto-conical driver diaphragm having a circular peripheral edge carrying an annular surround or suspension. Customarily, the circular small end of the frustoconical diaphragm supports a cylindrical voice coil former upon which is wound a conductive voice coil having positive and negative terminal ends. Conventional woofers utilize baskets which closely follow the frustoconical shape of the driver diaphragm and support the motor magnet and the circular diaphragm surround in a co-axial alignment, permitting a piston-like axial reciprocating movement of the diaphragm in response to electrical excitation of the voice coil.
In some high-end automotive applications, music aficionados and auto-sound competitors will install several woofers in a two-dimensional array on a baffle or enclosure surface; for example, it may be desirable to install four or six woofers in two rows of two or three, so mounting space becomes a concern. Another concern for music aficionados and auto-sound competitors is woofer failure due to thermal or mechanical overloading problems. Substantial amounts of power are required to provide competition-winning sound pressure levels, often well over 150 decibels (dB). Signals having such power require very large current flow through voice coil conductors, thus generating substantial amounts of heat, and drive the woofers to extreme excursions, thus generating extreme mechanical loads on diaphragms and suspensions. These concerns have led to ever-larger and more robust pistonic, cone-diaphragm woofer designs, as described in U.S. Pat. No. 6,938,726 (Roark et al), among others.
The specific elements making up this typical woofer have a well-established nomenclature. As illustrated in FIGS. 1 and 2, a typical direct radiating pistonic, cone-diaphragm woofer like that shown in U.S. Pat. No. 6,938,726 includes an electro-dynamic motor 14 with stationary parts and moving parts supported by the stationary parts. Typically, a woofer 10 has a stationary basket 11 which terminates at the upper end or distally in rigidly supported basket front flange 12 forming an annular or circular planar mounting surface. At the proximal end of basket 11 is a second substantially planar annular surface adapted to receive and carry woofer motor 14.
The moving cone or diaphragm 16 has an upper or distal larger circular edge upon which is permanently affixed a flexible half roll surround 18. Basket 11 is preferably cast from a rigid material such as a metal, preferably aluminum. Basket front flange 12 preferably carries a substantially planar ridged gasket ring 19, which is attached thereto by a plurality of evenly spaced threaded fasteners 40 which are evenly spaced around and completely penetrate through gasket ring 19 and are threadably received in blind holes machined into basket front flange 12 to clamp cone assembly surround 18 between gasket ring 19 and basket front flange 12. Rigid gasket ring 19 also includes an additional eight through holes or apertures evenly spaced between the apertures receiving hex fasteners 40 to permit longer threaded fasteners to penetrate through gasket ring 19 and through front flange 12 so that woofer 10 can be mounted in a baffle or enclosure wall, as is customarily done. Thus, front flange 12 has eight evenly spaced apertures, which penetrate completely through the planar front flange and also are aligned with similarly sized apertures in rigid gasket ring 19. Moving or reciprocating cone 16 typically carries a substantially dome-shaped dust cap 20 having a circular outer peripheral edge affixed (e.g. by a glue joint) to an exterior cone surface and the dust cap covers and protects a tube-shaped or substantially cylindrical voice coil former 12 which is affixed to a small opening of cone 16.
As is customary, at least one electrically conductive voice coil 26 having two ends (plus and minus) is wound around voice coil former 24; the voice coil ends (plus and minus) are each electrically connected to a single terminal connector 28 by a releasable electrical connection. Optionally, first and second voice coils are wound on former 24, and each voice coil has its ends terminated in a single terminal connector 28, and so four terminal connectors 28 are mounted on basket 11. Each of the terminals is carried by and supported on a horizontal and planar flange incorporated into basket 11 and the connective portions of each of the terminal connectors are electrically insulated from the rigid basket material by the use of insulating spacers or terminal bases which align and support the basket terminal connectors 28. Woofer motor 14 also includes a magnetic circuit defined by a doughnut shaped or annular ring shaped planar front plate 30, which along with the pole piece 32 defines a magnetic gap to focus magnetic flux from magnet 36 across voice coil 26. A substantially planar and circular back plate 34 also provides part of the magnetic circuit, carries cylindrical pole piece 32 and provides structural support for magnet 36. An annular magnetic gap focusing the magnetic flux from magnet 36 is defined in the annular space between pole piece 32 and the circular opening in front plate 30. The annular gap has a radial extent sized to receive the voice coil former's thickness plus the voice coil's thickness to provide adequate clearance for the moving voice coil in the magnetic gap during operation.
In use, the prior art Woofer's magnetic gap defined by the annular space between pole piece 32 and the circular opening in front plate 30 can be an area of substantial high temperature and voice coil heat is carried away from Woofer 10 by an air pumping action which accompanies motion of spider 22 whereby hot air surrounding voice coil 26 is pumped out to the side through screened side vents 38 arrayed around the side of Woofer 10 and defined in basket 11 just above or distally from woofer motor 14. The woofer cone assembly 16 includes a flexible spider suspension member 22 permanently affixed to the small proximal opening of cone 16 in close proximity to the joint between cone 16 and voice coil former 24. Spider suspension 22 comprises at least one accordion-pleated doughnut shaped annular ring of treated fabric which is attached (at the inside diameter of the spider circular aperture) to voice coil former 24 and cone 16 and (at the spider outer peripheral edge) carries a rigid spider ring 23. Spider ring 23 is optionally also made of a metal material, preferably aluminum, and the metal spider ring preferably is received in the spider plateau portion 46 of woofer basket 11. Basket 11 includes a circular valley having substantially straight sidewalls projecting transversely from the substantially planar plateau 46 to define a receptacle dimensioned to center and support the spider ring 23.
Basket 11 has distal outer or front flange 12 with the peripheral edge adapted to carry gasket ring 18 and has a proximal inner support surface or plateau spaced apart from the distal outer flange 12 by a distance (along the cone central axis) roughly equal to the front-to-back depth of cone 16. The basket spider valley is comprised of the planar plateau 46 and the perpendicular sidewall 45 projecting upwardly from the plateau 46. Together, basket valley sidewall 45 and basket plateau 46 define a receptacle which receives, centers and supports the spider ring 23. Spider suspension 22 preferably comprises a bulky layer treated fabric spider element permanently bonded with a glue joint to voice coil former 24 proximate the junction with cone 16 and bonded at its outer peripheral edge to spider ring 23 in a glue joint or the like. Referring now to FIG. 2, spider ring 23 is optionally an annular ring and spacer which attaches to two three-layer spiders, one-three layer spider is glued to the top of spider ring 23 and one three layer spider is spaced apart from the first and is glued to the bottom of ring 23. Spider ring 23 fits in and is centered on basket spider plateau 46. As best seen in FIG. 2, spider ring 23 has a selected proximal-to-distal (or lower to upper) thickness defined between a proximal (motor side) surface and a distal (cone side) surface and distal three layer annular spider 22a is connected to spider ring 23 adjacent the distal surface, while the proximal three layer annular spider 22b is connected to the spider ring 23 adjacent the proximal surface of spider ring 23, a distance roughly corresponding to the thickness of spider ring 23. As noted above, woofer 10 optionally includes 2 voice coils, one layered on top of the other on voice coil former 24 and each of the 2 voice coils is preferably of a standard (e.g. four ohm) impedance and is terminated in first and second voice coil lead terminals.
Thus, the typical prior art woofer has a well understood electro-dynamic motor assembly 14 using at least one voice coil to reciprocally drive at least one transducer diaphragm in a fore and aft or in and out pistonic motion which radiates sound directly into an ambient space. These typical direct radiating low frequency transducer designs have not really proven satisfactory for many audio system designers and audio enthusiasts.
Others have attempted to use rotary or rotating vane structures driven by rotating motor structures such as rotating commentator motors or rotating servomotors (i.e., rotor within stator motors) such as are disclosed in U.S. Pat. Nos. 4,564,727, 4,763,358 (Danley et al) or U.S. Pat. No. 5,825,901 (Hisey), but these low frequency transducer systems have, not found favor in the marketplace, possibly because of the complexity, cost and weight associated with motors having rotating armatures (e.g., rotors) within stators. There is a need, therefore, for a simpler and more compact transducer structure and a method for configuring and installing one or more transducers.